Stents, covered stents (i.e., stent-grafts), occluders and filters are commonly used in the treatment of vascular disease, for the creation of shunts between various organs and vessels of the body, for exclusion or sealing of branch vessels or structural defects, and for the reduction of adverse events associated with interventional procedures.
Stents are commonly manufactured from filaments. Nitinol wire is a preferred material given its shape memory properties and excellent history as a material used in implantable devices. Expanded polytetrafluoroethylene (ePTFE) and Dacron® materials are commonly used to cover the stents to create stent-grafts. Covering materials serve to prevent blood passage through the wall of the device and to inhibit the invasion of host tissue or fluids into the lumen of the device. They also are used to isolate aneurysmal vessel pockets from the bloodstream thereby preventing vessel rupture and embolization of plaque or thrombus.
Self-expanding stents and covered stents constructed of filaments are formed by either weaving or braiding multiple filaments. Device removal is imperative in the event of unintentional occlusion of a vessel side-branch, improper device deployment, or if the device is inappropriately sized with respect to the treated vessel segment. Alternatively, devices can be snared and pulled into a catheter or through the vasculature to an access site thereby resulting in the potential for significant damage to the vessel lumen. In instances where significant tissue ingrowth has occurred, removal of such devices is accomplished by the painstaking and time consuming process of removing one filament at a time by pulling on one of its ends. Surgical removal is sometimes necessitated, an outcome that the use of a stent or covered stent is intended to obviate in the first place.
For safety and device durability reasons, both ends of each filament must be secured in some fashion. The design and manufacturing process must guard against the filaments becoming unwoven in use, for instance. This risk must be addressed in the design and construction of the device. As the number of individual filaments in the device increases, the risk of wire pattern disruption at the filament terminations correspondingly increases.
Wallsten, in U.S. Pat. No. 4,655,771, teaches a prosthesis for intraluminal implantation comprising a diametrically expandable or compressible tubular body. This device is preferably a braided tube comprised of flexible and elastic thread elements. When radially compressed and constrained from returning to its original diameter, the inherent self-expansion of this device imparts a hoop force on the wall of the lumen. The patent teaches the formation of crossover points in interlocking relationships, typical of braided structures. The crossover points may optionally be bonded together. Wallsten does not teach the removal of such devices by pulling on the end of a single filament. No teaching is provided for using such a stent to create an occluder device.
Schmitt, in U.S. Pat. No. 5,443,499, teaches a radially expandable tubular prosthesis constructed with yarns that are deformable under dilatation pressures generated by balloon catheter devices. The expansion is achieved by drawing of the yarn within its elastic deformation region or plastically deforming it beyond its yield point. No teaching is presented regarding the use of a resilient filament material that would impart self-expanding properties to the endoprosthesis were it to be radially compressed. The tubular prostheses described therein do not serve the function of a stent or covered stent since they require the addition of a stent fixation device for intraluminal delivery and placement. Also, endoprosthesis plus the stent are not removable by pulling on the end of a single filament and the patent provides no teaching whatsoever regarding the creation of occluder devices.
Myers et al., in U.S. Pat. No. 5,735,892, teach an intraluminal stent graft. The stent graft is comprised of a stent element to which an ePTFE covering is affixed to the exterior surface, the interior surface, or both surfaces of the stent. The stent may be self-expanding or balloon-expandable. The covering can be affixed by an adhesive, preferably fluorinated ethylene propylene (FEP). One embodiment takes the form of a braided structure that employs alternating strand crossover points.
U.S. Pat. No. 6,007,574 and US Published Application 2004/0167611 to Pulnev et al. teach interwoven, interlaced stent devices. They also teach the construction of occlusion devices from these stents. Pulnev et al. do not teach bonding of crossover points.
Kotula et al., in U.S. Pat. No. 5,725,552, and Amplatz, U.S. Pat. No. 6,638,257, teach occlusion devices formed by braiding strands of metal, such as nickel-titanium alloys. The ends of the strands are gathered and held together. These devices are devoid of central orifices through which guidewires could be inserted. The latter patent further teaches the use of a PTFE fabric band around the device periphery in order to inhibit tissue ingrowth. U.S. Pat. No. 6,123,715 to Amplatz teaches the manufacture of similar braided and gathered occlusion devices made of wires such as nitinol.